great in theory, but have you seen the mess you can make in a hopper by just shaking it a little too hard??
now imagine a big bog/box of paintballs on your back, now run with them. youd end up with a nice bag of paint n shells but not paintballs.
also imagine if the feed tube got blocked with a slightly dodgy paintball? that would be an absolubt nightmare to clear.
sorry to ruin a dream